Development of a Semi-continuous Set-up for Catalytic Hydrotreatment of Lignin

Depletion of fossil fuels and the ongoing production of greenhouse gasses have led to an increased demand of renewable energy, transportation fuels and chemicals. Whereas energy can be produced by using wind and solar power, chemicals need a carbon containing source. Biomass is the only sustainable source of carbon available at the moment for producing chemicals. Lignocellulosic biomass is the woody part of biomass and is made out of three main components, being cellulose, hemicellulose and lignin. Lignocellulosic biomass does not compete with food and has enormous potential as a feedstock for second generation bio-fuels and chemicals. This study focuses on a specific part of lignocellulosic biomass, namely lignin. Lignin has an enormous potential for the production of fuels and bulk chemicals, due to its aromatic structure [1]. Aromatic structures are valuable, because of the high demand of phenols and benzene, toluene and xylene (BTX). This study focuses on the valorization of lignin with the use of heterogeneous catalysis and hydrogen under elevated conditions (100-160 bar and 400°C). The objective of this study was to develop an optimal semi-continuous set-up for catalytic hydrotreatment of lignin towards phenolic and aromatic products. A catalytic screening, pressure optimization and influence of reaction time were performed. Five catalysts were found to be suitable for the catalytic hydrotreatment of lignin. Total aromatic and phenolic yield was in the following order Ru/TiO2 (12.9%) (ruthenium chloride made) > Ru/TiO2 (12.0%) (ruthenium acetate made) > Cat. D (11.9%) > Ru/C (11.4%) > Pd/C (8.1%). Ruthenium on titania (ruthenium chloride made) therefore was the most suitable catalyst for maximizing the total phenolic and aromatic yield. Light oil yield is very important in semi-continuous catalytic hydrotreatment of lignin. Combining total phenolic and aromatic yield with the light oil yield, ruthenium on carbon was found to be the most suitable catalyst. At 130 bar the light oil yield for ruthenium on carbon was the highest, 15.7%. Therefore 130 bars was found to be the optimal pressure for the semi-continuous catalytic hydrotreatment of lignin with ruthenium on carbon. Reaction time had large influence on the amount of light oil produced for a ruthenium on carbon catalyst, it increased over time (2.2% at 0.5 h to 28.9% at 8 h). Water amount also increased over time, where the oil yield decreased with about the same amount (75.0% at 0.5 h to 54.0% at 8 h). Product elemental composition showed that the amount of oxygen was decreasing in the heavy oil and 0.22wt% at 8 h of reaction time. ALCELL lignin contains for 28.9wt% of oxygen. Total phenolic and aromatic yield increased with reaction time to a maximum at 4 h, from 5.3% at 0.5 h to 14.2% at 4 h.